Through transcriptome analysis with publically available RNA-Seq data, we have identified one gene signature that can predict BET bromodomain inhibitor-sensitive and -resistant small cell lung cancer cell lines with 100% specificity. We have made significant progress in understanding the molecular features in association with the predictive biomarker that makes small cell lung cancer cells more sensitive to BETi. Finally, a collaboration with Boehringer Ingelheim has been established to validate the effectiveness of identified predictive biomarker in small cell lung cancer patients treated with its BET inhibitor.